Apparatus for transferring electrostatic latent images in electrophotographic copiers of image transfer type

ABSTRACT

An apparatus comprising a photosensitive element to be driven for charging and exposure to form an electrostatic latent image on its surface and having a grounded electroconductive backing on its rear face, a transfer roller adapted to bring the dielectric surface of copy paper into intimate contact with the surface of the photosensitive element and to ground the electroconductive backing of the paper for electrical connection with the conductive backing of the photosensitive element, disconnecting means for breaking electrical connection between the roller and the conductive backing of the element through grounding while the paper is not positioned between the element and the roller, and means for grounding the conductive backing of the paper after the paper has passed through a transfer station, so as to prevent discharge due to the breakdown of air gap between the transfer roller and the photosensitive element for the protection of the charge retaining surface of the element. The transfer roller has means for selectively breaking the electrical connection between the two backings for use with copy papers of varying sizes.

United States Patent [191 Tanaka et al.

[ Aug. 6, 1974 [75] Inventors: Susumu Tanaka, Sakai; Yuji Enoguchi,Higashi-Osaka; Takao Fujiwara, Sakai, all of Japan [73] Assignee:Minolta Camera Kabushiki Kaisha,

Osaka, Japan [22] Filed: Mar. 7, 1973 [21] Appl. No.: 338,784

[30] Foreign Application Priority Data OTHER PUBLICATIONS Oldeboom,Electromechanical Transfer Mechanism, IBM Technical Disclosure Bulletin,Vol. 1, No. 3, DP. 4 & 5.

Primary Examiner-Samuel S. Matthews Assistant Examiner-Kenneth C.Hutchinson Attorney, Agent, or Firm-Wolder & Gross [5 7] ABSTRACT Anapparatus comprising a photosensitive element to be driven for chargingand exposure to form an electrostatic latent image on its surface andhaving a grounded electroconductive backing on its rear face, a transferroller adapted to bring the dielectric surface of copy paper intointimate contact with the surface of the photosensitive element and toground the electroconductive backing of the paper for electricalconnection with the conductive backing of the photosensitive element,disconnecting means for breaking electrical connection between theroller and the conductive backing of the element through grounding whilethe paper is not positioned between the element and the roller, andmeans for grounding the conductive backing of the paper after the paperhas passed through a transfer station, so as to prevent discharge due tothe breakdown of air gap between the transfer roller and thephotosensitive element for the protection of the charge retainingsurface of the element. The transfer roller has means for selectivelybreaking the electrical connection between the two backings for use withcopy papers of varying sizes.

8 Claims, 10 Drawing Figures PAIENIEDMIB 61914 3.827. 800

SHEET 1 [IF 2 Fig.7 PRIOR ART. (b

BACKGROUND OF THE INVENTION The present invention relates to anapparatus for transferring electrostatic latent images inelectrophotographic copiers of the electrostatic latent image transfertype, more particularly to an apparatus for transferring electrostaticlatent images which comprises a photosensitive element to be subjectedto charging and exposure to form an electrostatic latent image on itsdielectric surface layer and an electroconductive transfer roller forbringing the dielectric surface layer of an electrostatic image receptorsuch as copy paper into intimate contact with the dielectric layer ofthe photosensitive element and in which a support member supporting therear face of the photosensitive element and the transfer roller aregrounded respectively to electrically connect the electroconductivebacking of the photosensitive element to the electroconductive backingof the copy paper and to thereby transfer the electrostatic latent imageon the photosensitive element to the copy paper at an area where thedielectric layer of the paper comes into intimate contact with thedielectric layer of the photosensitive element. Thereafter, inaccordance with the general practice, a toner powder is applied to theelectrostatic image bearing face of the copy paper which is then heatedto fuse the toner powder and form a permanent image.

With the electrophotographic copiers of the type described, thephotosensitive element has a charge retaining area which is somewhatlarger than the area of copy paper of a maximum size usable.Accordingly, in the case where a sheet of copy paper is used which hasbeen previously cut to a specified size, part of the charged surface ofthe photosensitive element will be left uncovered by the paper duringthe transfer of image.

As indicated by hatching in FIG. 1 (a), the charged surface, namely thecharge retaining surface A of a photosensitive element 2, is larger thana sheet of copy paper 1 of a maximum size. Even if the length of agrounded electroconductive transfer roller 3 is equal to the width ofcopy paper I, the roller 3 will come into direct contact with the chargeretaining surface A of the photosensitive element twice when the paper 1advances as shown in FIG. 1 (b), namely when the front end of the paperalmost reaches the position of the roller 3 (see the phantom line) andwhen the rear end of the paper has passed the position of the roller 3(see the solid line), breaking the insulation of the air gap uponcontact to cause a very intense discharge, since the charge retained onthe photosensitive element 2 is at a high voltage level whereas theroller 3 is grounded. Moreover, inasmuch as the impedance due to theelectrical connection between the transfer roller 3 and the backing ofthe photosensitive element 2 is low, the abovementioned discharge takesplace within a very short period of time at an extremely high currentdensity.

Consequently, the dielectric layer of the photosensitive element 2 willbe damaged by ion bombardment or chemically affected by ions. Further ifit locally includes a point of low insulation, ions will concentrate atthat point to damage the dielectric surface. When thus damaged, thedielectric layer locally fails to retain charges thereafter placedthereon, rendering the developed image defective and no longer assuringa satisfactory copying operation.

The same problem will be also experienced with the use of copy paper 1of a smaller size. In this case, the

detrimental phenomena are not restricted to the vicinities of the frontand rear ends of advancing paper 1'. As illustrated in FIGS. 2 (a) and 2(b), the opposite ends of the roller 3 extend beyond the opposite edgesof the paper 1 during the transfer operation and face the chargeretaining surface A of the photosensitive element 2. Since the thicknessof the copy paper 1' is up to a maximum of to microns, dielectricbreakdown will take place across an air gap S on the opposite sides ofthe paper 1, causing a discharge at high current density to damage anddestroy the dielectric surface layer of the photosensitive element 2.Such damage and destruction of the photosensitive surface seriouslydeteriorate the photosensitive element 2 and exert an adverse effectover an area including more or less inner portions of the surface of alarge sheet of copy paper.

SUMMARY OF THE INVENTION An object of this invention is to eliminate anydis charge of large current due to the dielectric breakdown of a smallair gap between the surface of a photosensitive element and anelectroconductive transfer roller when copy paper is not positionedtherebetween, the roller being positioned in proximity to the surfacewith the air gap interposed therebetween and also adapted for contactwith the photosensitive surface for the transfer of an electrostaticlatent image, so as to render the photosensitive surface free fromdamage and destruction and to thereby permit the photosensitive elementto function as intended over a long period.

Another object of this invention is to prevent discharges due to thebreakdown of an air gap produced between the copy paper and thephotosensitive surface under the influence of a residual electric fieldpossessed by the electroconductive backing of the copy paper when therear end of the paper is peeled off the photosensitive surface after thetransfer of the electrostatic latent image so as to protect thephotosensitive surface from damage and destruction due to thedischarges.

Another object of this invention is to prevent the above-mentioneddischarge irrespective of the size of the copy paper.

According to this invention there is provided disconnecting means forisolating a circuit electrically connecting the electroconductivebacking of a photosensitive element to an electroconductive transferroller and operable to break the electrical connection while copy paperis not positioned between the photosensitive element and the transferroller.

The disconnecting means mechanically moves the transfer roller toward oraway from the photosensitive element in operative relation to theadvance of the copy paper or of the photosensitive element so as to keepthe transfer roller retracted, while the paper is not positioned betweenthe photosensitive element and the transfer roller, at a safe positionsuch that the dielectric breakdown of an air gap therebetween will nottake place.

According to another embodiment of the disconnecting means, the circuitelectrically connecting the backing of the photosensitive element to thetransfer roller includes a switch for opening and closing the circuit inoperative relation to the advance of the transfer paper or of thephotosensitive element, so that while the paper is not positionedbetween the photosensitive element and the transfer roller the switchwill be opened to electrically disconnect the transfer roller from theground. In this case, there is no need to advance or retract thetransfer roller mechanically.

In this way, the dielectric breakdown of the air gap is completelyeliminated between the photosensitive element and the transfer roller byvirtue of the presence of paper therebetween and by the disconnectingmeans while the paper is not positioned therebetween.

However, the grounding of the transfer roller serves to discharge thecharge on the electroconductive backing of the copy paper to the earth,thereby preventing the paper from being attracted to the photosensitivesurface by the electrostatic attraction. If the transfer roller isretracted to a safe position permitting no discharge or is electricallydisconnected from the earth upon completion of charge transfer, theelectroconductive backing la (see FIG. 3) of the paper 1 will have inthe vicinity of its rear end a residual charge of polarity opposite tothat of the charge on the photosensitive surface, with its dielectriclayer lb still attracted to the photosensitive surface. Subsequently,the moment when the advancing paper 1 is separated from thephotosensitive surface, the resulting small air gap will be subjected todielectric breakdown by the field of the residual charge to permitdischarge.

The present invention further provides means for eliminating suchdischarge. Thus there is provided electroconductive grounding meansspaced apart from the transfer roller by a suitable distance in parallelthereto to ground the electroconductive backing of the copy paper afterit has passed over the transfer roller and to thereby discharge theresidual charge thereon to the earth. If the conductive backing has anelectric resistivity of the order of 10 to 10 ohms as is usally the casewith copy papers for the transfer of electrostatic latent images, theresidual charge on the backing of the paper at its rear end will besatisfactorily returned to the earth by the grounding means asthe paperis out of contact with the grounded transfer roller. The grounding meansserves also as a guide for the paper after it has passed over theroller.

According to this invention, the transfer roller further comprises anassembly of a center portionand opposite end portions electricallyinsulated from the center portion, the roller thus being adapted for usewith copy papers of varying widths. The center portion and the oppositeend portions are grounded by individual means, respectively, each ofwhich has disconnecting means. If the copy paper is of a small width,the center portion alone of the transfer roller will be grounded onlywhile the paper is positioned between the transfer roller andphotosensitive element, the other portions of the roller beingdisconnected from earth electrically. For papers of large widths, thecenter portion and opposite end portions are all grounded only duringthe transfer operation.

The construction comprising the center portion and the end portionselectrically insulated therefrom may BRIEF DESCRIPTION OF THE DRAWINGSFIGS. 1 (a), (b) and FIGS. 2 (a), (b) are views illus- -trating only thetransfer station of an electrophotographic copier of the electrostaticlatent image transfer type, FIG. 1 (b) and FIG. 2 (b) being sideelevations of FIG. 1 (a) and FIG. 2 (a) respectively;

FIG. 3 is a view illustrating copy paper at the transfer station as thepaper isabout to be released;

FIG. 4 is a view illustrating only the transfer stationof an embodimentof this invention;

FIG. 5 is a view illustrating another embodiment of this invention andcorresponding to FIG. 4;

FIG. 6 is a similar view illustrating another embodiment of thisinvention;

FIG. 7 is a view illustrating the transfer station of another embodimentof this invention which includes means for grounding the back of thecopy paper;

FIG. 8 is a view illustrating another embodiment of the presentinvention and corresponding to FIG. 7;

FIG. 9 is a front view partly in section showing the construction of theprincipal part of a transfer roller employed in the embodiment of FIG.8; and

FIG. l0 is a front view of a grounding roller.

DESCRIPTION OF THE PREFERRED 1 EMBODIMENTS FIG. 4 shows an embodiment inwhich a transfer roller 3 is adapted to be mechanically retracted fromthe surface of a photosensitive element 2 so that from the moment asheet of copy paper 1 passes between the roller 3 and the photosensitiveelement-2 until the next sheet of paper is sent in between the roller 3and the photosensitive element 2, the air gap between the roller 3 andthe photosensitive element 2 will remain large to prevent dielectricbreakdown notwithstanding the high voltage on the surface ofphotosensitive element 2 and the grounding of the transfer roller 3.

The photosensitive element 2 is supported on a drumlike support 2a whichis grounded to ground the electroconductive backing of thephotosensitive element. Similarly, the transfer roller 3 has its shaftgrounded and is pressed against the rear face of copy paper 1 by aspring 4 during a transfer operation, whereby the dielectric surface ofthe copy paper 1 is brought into intimate contact with the chargedsurface of the photosensitive element 2 to provide an air gaptherebetween which will permit latent image transfer. At the same time,the roller grounds the conductive backing of the copy paper 1.Consequently, the conductive backings of the photosensitive element 2and the paper 1 are electrically connected to each other by theabove-mentioned grounding. The intimate contact of the dielectricsurface of the paper 1 with the charge surface of the element 2 permitsan electrostatic latent image on the photosensitive element 2 to betransferred to the paper 1. which may then be treated in the usualmanner such as by applying a powdered toner to the image bearing face ofthe paper 1 and heat fusing the toner to form a permanent imagecorresponding to the electrostatic latent image.

A cam 5 fixed to the support 2a is in itself made of an electricallyhighly insulating material or has a construction having high insulatingproperties. The cam has a circumferential length such that while thepaper 1 is not positioned between the photosensitive element 2 and thetransfer roller 3 during the rotation of the photosensitive element 2and the advance of the paper 1 in timed relation thereto, the cam willshift the transfer roller 3 away from the influence of the element 2against the spring 4 and retain the same at a retracted position torender the air gap free from dielectric breakdown as already described.Thus discharges which would otherwise result from the proximity of thetransfer roller 3 to thephotosensitive surface are precluded in thecopier for use with copy paper of a definite size.

FIG. 5 shows an embodiment comprising a photosensitive element 2 in theform of a belt, a drive roller 7 supporting the element 2, a transferroller 3 biased by a spring 4 for bringing copy paper 1 into intimatecontact with the element 2, and reciprocally driving means such as aplunger 6. While the paper 1 is not positioned between thephotosensitive element 2 and the transfer roller 3, the plunger 6 keepsthe transfer roller 3 away from the surface of the element 2 to providea sufficient air gap therebetween to prevent the aforementioneddielectric breakdown.

The plunger 6 may be operated by electromagnetic, hydraulic or any othersuitable means to be controlled by detectors such as microswitches fordetecting the front and rear ends of paper 1 during its advancingmovement. The transfer roller 3 and the drive roller 7 are of courseelectrically grounded.

The embodiment shown in FIG. 6 has a switch 9 included in a groundingcircuit 8 for an electroconductive transfer roller 3. The switch 9 isopen during the absence of paper 1 between the transfer roller 3 and aphotosensitive element 2 to disconnect the transfer roller 3 from theground and to thereby substantially prevent the injection of a chargefor transfer.

According to this embodiment, the transfer roller 3 is always urgedtoward the element 2 by unillustrated means to bring the dielectricsurface of copy paper 1 close to the charged surface of the element 2 toprovide an air gap therebetween required for the image transfer. Whilethe paper 1 is not positioned between the roller 3 and the element 2,the roller 3 is in rolling contact with the photosensitive surface. Thesupport for the transfer roller 3 is of course insulated electrically.The operation of the switch 9 is controlled electromagnetically ormechanically in the same manner as above.

It will be apparent from the above that the mechanical or electricaldisconnecting means 0 (specifically indicated at 5, 6 or 9) forretracting or ungrounding the conductive transfer roller 3 eliminatesthe electrical condition which permits a discharge between the transferroller 3 and the photosensitive element 2 while the paper 1 is notlocated at the transfer station, i.e. between the element and theroller. More specifically, such effect is achieved by the mechanicalmeans which forms a greater gap between the roller 3 and the element 2,or by the electrical means which disconnects the roller 3 from theground. Therefore despite the presence of charged surface of thephotosensitive element 2 which is not covered with the paper 1, theexposed area will be renderedfree from any discharge.

Due to the elimination of the electrical action between the roller 3 andthe photosensitive element 2 achieved by the disconnecting means 0, therearv end of the paper 1 passing through the transfer station carries aresidual charge induced by the electrostatic latent image on thephotosensitive element 2 as already described with reference to FIG. 3,with the result that the electric field of the residual potential givesrise to dielectric breakdown of the gap to cause discharge again whenthe rear end separates from the photosensitive surface. This results infogging of the developed image. FIG. 7 shows means for eliminating suchdetrimental result.

With reference to FIG. 7, an electroconductive roller 10 is disposedbeside the path of travel of copy paper 1 in contact with the conductivebacking 1a of the paper 1, the roller 10 thus serving as grounding meansE for the backing la. FIG. 7 does not illustrate disconnecting means 0for retracting a transfer roller 3 or disconnecting the same from theearth when the rear end of the paper 1 passes through the transferstation.

Since the grounding means E serves to ground the conductive backing laof the paper 1 when the paper 1 separates from the photosensitiveelement 2, the means may be in the form of a conductive roller asdescribed or in the form of an elastic tonguelike member, or it may beany other grounding member which is positioned beside the path ofadvance of the paper 1 passing through the transfer station and which iscapable of grounding the backing la. As already described, the groundingmeans E serves also as a guide for the paper 1.

As illustrated in FIG. 7, the grounding means E grounds the conductivebacking la of the paper 1 when the paper 1 is to be separated from thephotosensitive element 2, with the transfer roller 3 retracted to a safeposition to prevent the dielectric breakdown of the air gap between theroller 3 and the element 2, so that the foregoing operation of thedisconnecting means 0 permits the residual charge (indicated as symbolsin the drawing) on the conductive backing of the paper 1 to be returnedto the earth by way of the grounding means E such as the conductiveroller 10. As a result, the field of residual charge will be nullifiedwhen the paper 1 is separated from the photosensitive element 2 and theaforementioned discharge will not take place, consequently rendering thedeveloped image free from fogging attributable to such discharge.

The distance between the transfer station and the position where thegrounding means E contacts the conductive backing la of the copy paper 1is so determined that the foregoing function can be fully performed withthe electric resistivity of the element 1a taken into consideration. Ifthe electric resistivity of the backing element la is of the order of 10to 10 ohms as is generally the case with this type of paper, it isperfectly possible to return the residual charge from the rear end ofthe conductive backing la to the earth when the paper 1 is separated,without permitting the discharge to take lace.

p FIGS. 8 to 10 show another embodiment of this invention adapted foruse with copy papers of different widths. In the case where paper 1 of asmall width is used for copying, this embodiment eliminates dielectricbreakdown that would otherwise occur between a transfer roller 3 and aphotosensitive element 2 at the opposite sides of the paper.

The electroconductive transfer roller 3 comprises a center portion 3ahaving alength corresponding to the width of paper of a small size andother portions 3b electrically insulated from the center portion. Therespective portions 3a and 3b are grounded by way of separate circuitsl1 and 12 for electrical connection with the conductive backing of thephotosensitive element 2 individually. The circuits 1] and 12 includeswitches 13 and 14, respectively, which serve as disconnecting means foropening and closing the circuits individually. Opening of the switches13 and 14 disconnects the portions 3a and 3b from the earthelectrically. FIG. 9 shows that the center portion 3a of the transferroller 3 is connected to the circuit 11 at its shaft 3a.

The opposite end portions 3b are secured to and shortly spaced from thecenter portion 3a by electrical insulators interposed therebetween andare connected to the circuit 12 by way of contact members 3b. Incooperation with an auxiliary roller 16 made of an electrical insulator,a conductive roller 10 serving as grounding means E guides the paper 1discharged from the transfer station.

If copy paper 1 of a small size is used, the switch 13 for grounding thecenter portion 3a only is held closed while the paper 1 is positioned inthe transfer station, with the switch 14 left open to keep the oppositeend portions 3b out of connection with the ground (see FIG. 8) wherebythe injection of charge to transfer an electrostatic latent image willbe achieved only through the center portion 3a. Since the end portions3b are out of connection with the ground, there is no possibility of adischarge taking place across the air gap between the portions 3b andthe charged surface of the photosensitive'element 2.

If copy paper 1 of a large size is used, both switches 13 and 14 areheld closed while the paper 1 is positioned in the transfer station,with the result that the image will be transferred onto the entiresurface of the paper 1.

The transfer roller 3 may comprise a greater number of segments than inthe foregoing embodiment for use with copy papers of varying widths, thesegments being joined together in electrically insulated fashion andprovided with grounding circuits, respectively, which are opened andclosed individually.

Although the disconnecting means 0 described above for preventingdischarges has such construction that the switches 13 and 14 are openedand closed, the respective portions may alternatively be separated andadapted for forward and backward movement individually so as to preventthe abovementioned discharges mechanically.

The disconnecting means 0 can be operated, without any difficulty, intimed relation to the rotation of the photosensitive element and to theadvance of the copy paper, for example, by providing a detector forsensing the rear end of the paper or by any other means generally known.

What is claimed is:

1. An apparatus in an electrostatic copying machine for transferring anelectrostatic latent image to a receptor member having a dielectriclayer and a conductive layer comprising:

a photosensitive element having a chargeable surface exposable to alight image to form thereon an electrostatic latent image and includinga grounded conductive backing element,

a conductive transfer roller for transferring the electrostatic latentimage to the dielectric face of said receptor member by bringing thedielectric layer into intimate contact with the surface of thephotosensitive element,

said transfer roller being in contact with said conductive layer of thereceptor member during the transfer of the electrostatic latent imageand being grounded so as to electrically connect the conductive backingelement with the transfer roller through said conductive layer,

disconnecting means for breaking the electrical connection between saidtransfer roller and said conductive backing element in the absence of areceptor member between said transfer member and said photosensitiveelement for preventing dielectric breakdown, and

means following the transfer roller for grounding the conductive layerof the receptor member bearing a transferred electrostatic latent imageso as to dissipate the remaining charges.

2. The apparatus as set forth in claim 1 wherein the disconnecting meanscomprises mechanically operative means for holding the transfer rolleraway from the photosensitive element while a receptor is not positionedbetween the photosensitive element and the transfer roller so as to keepan air gap between the element and the roller sufficiently wide toprevent a dis charge due to the dielectric breakdown of the gap.

3. The apparatus as set forth in claim 2 wherein the operative meanscomprises a member for biasing the transfer roller toward thephotosensitive element and a cam for keepingthe transfer rollerretracted from the photosensitive element against the action ofthebiasing member while a receptor is not positioned'between thephotosensitive element and the transfer roller."'

4. The apparatus as set forth in claim 2 wherein the operative meanscomprises a member for biasing the} transfer roller toward thephotosensitive element and a reciprocating mechanism for keeping thetransfer roller retracted from the photosensitive element while areceptor is not positioned between the photosensitive element and thetransfer roller upon detecting the absence of the receptor therebetween.

5. The apparatus as set forth in claim 1 wherein the disconnecting meansincludes a switch for opening a grounding circuit of the transfer rollerin the absence of a receptor between the photosensitive element and thetransfer roller upon detecting the absence of the receptor therebetween.

6. The apparatus as set forth in claim 1 wherein the grounding meanscomprises an electroconductive grounding roller to be brought intorolling contact with the conductive backing of the receptor after thereceptor has passed from between the transfer roller and photosensitiveelement.

7. The apparatus as set forth in claim 1 wherein the conductive transferroller comprises an assembly of a plurality of coaxial end to endsections so as to be usable for copy papers of varying widths, thesections being insulated from one another and grounded individually forconnection with the conductive backing of the photosensitive element,the sections being selectively disconnectable from the ground toselectively break their electrical connection with the conductivebacking of the photosensitive element.

8. In an electrostatic copying machine a mechanism for producing anelectrostatic latent image on the dielectric front face of an imagereceptor having an electrically conductive rear substrate comprising aphotosensitive element having an electrically conductive backing, saidphotosensitive element being electrically chargeable and exposable to alight image to produce on the surface thereof a latent electrostaticimage, a transfer member having an electrically conducting face andurged toward engagement with said photosensitive element, said imagereceptor being advanceable along a path between said photosensitiveelement and said transfer member with its front face engaging saidphotosensitive element and its rear substrate engaging said transfermember, means responsive to the presence of member to saidphotosensitive element backing.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION-PATENT NO. 3,827, 800 A DATED August 6, 1974 INVIENTOR(S) SUSUMO TANAKA,et a1 It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

"[75] Inventors: Susumu Tanaka, Sakai; Yuji Enoguchi, Higashi-Osaka;Takao Fujiwara, Sakai; Isao Iizaka, Toyokawa; Toshio Yamamoto, Toyokawa,all of Japan-- Signed and Sealed this T wenty-eighth D a) of February I978 [SEA L] Attest:

RUTH C. MASON LUTRELLE F. PARKER Arresting Oflicer Acting Commissionerof Patents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICECERTIFICATE OF CORRECTION 9 PATENT N0. 3 827 800 DATED August 6 1974 INVENTOR(S) SUSUMO TANAKA, et a1 It is certified that error appears in theabove-identified patent and that said Letters Patent Q are herebycorrected as shown below:

"[75] Inventors: Susumu Tanaka, Sakai; Yuji Enoguchi, Higashi-Osaka;Takao Fujiwara, Sakai; Isao Iizaka, Toyokawa; Toshio Yamamoto,

Q Toyokawa, all of Japan-- Signed and Scaled this Twenty-eighth ofFebruary I 978 [SEAL a 1 Arrest:

RUTH C. MASON LUTRELLE F. PARKER Arresting Officer Acting Commissionerof Patents and Trademarks O

1. An apparatus in an electrostatic copying machine for transferring anelectrostatic latent image to a receptor member having a dielectriclayer and a conductive layer comprising: a photosensitive element havinga chargeable surface exposable to a light image to form thereon anelectrostatic latent image and including a grounded conductive backingelement, a conductive transfer roller for transferring the electrostaticlatent image to the dielectric face of said receptor member by bringingthe dielectric layer into intimate contact with the surface of thephotosensitive element, said transfer roller being in contact with saidconductive layer of the receptor member during the transfer of theelectrostatic latent image and being grounded so as to electricallyconnect the conductive backing element with the transfer roller throughsaid conductive layer, disconnecting means for breaking the electricalconnection between said transfer roller and said conductive backingelement in the absence of a receptor member between said transfer memberand said photosensitive element for preventing dielectric breakdown, andmeans following the transfer roller for grounding the conductive layerof the receptor member bearing a transferred electrostatic latent imageso as to dissipate the remaining charges.
 2. The apparatus as set forthin claim 1 wherein the disconnecting means comprises mechanicallyoperative means for holding the transfer roller away from thephotosensitive element while a receptor is not positioned between thephotosensitive element and the transfer roller so as to keep an air gapbetween the element and the roller sufficiently wide to prevent adischarge due to the dielectric breakdown of the gap.
 3. The apparatusas set forth in claim 2 wherein the operative means comprises a memberfor biasing the transfer roller toward the photosensitive element and acam for keeping the transfer roller retracted from the photosensitiveelement against the action of the biasing member while a receptor is notpositioned between the photosensitive element and the transfer roller.4. The apparatus as set forth in claim 2 wherein the operative meanscomprises a member for biasing the transfer roller toward thephotosensitive element and a reciprocating mechanism for keeping thetransfer roller retracted from the photosensitive element while areceptor is not positioned between the photosensitive element and thetransfer Roller upon detecting the absence of the receptor therebetween.5. The apparatus as set forth in claim 1 wherein the disconnecting meansincludes a switch for opening a grounding circuit of the transfer rollerin the absence of a receptor between the photosensitive element and thetransfer roller upon detecting the absence of the receptor therebetween.6. The apparatus as set forth in claim 1 wherein the grounding meanscomprises an electroconductive grounding roller to be brought intorolling contact with the conductive backing of the receptor after thereceptor has passed from between the transfer roller and photosensitiveelement.
 7. The apparatus as set forth in claim 1 wherein the conductivetransfer roller comprises an assembly of a plurality of coaxial end toend sections so as to be usable for copy papers of varying widths, thesections being insulated from one another and grounded individually forconnection with the conductive backing of the photosensitive element,the sections being selectively disconnectable from the ground toselectively break their electrical connection with the conductivebacking of the photosensitive element.
 8. In an electrostatic copyingmachine a mechanism for producing an electrostatic latent image on thedielectric front face of an image receptor having an electricallyconductive rear substrate comprising a photosensitive element having anelectrically conductive backing, said photosensitive element beingelectrically chargeable and exposable to a light image to produce on thesurface thereof a latent electrostatic image, a transfer member havingan electrically conducting face and urged toward engagement with saidphotosensitive element, said image receptor being advanceable along apath between said photosensitive element and said transfer member withits front face engaging said photosensitive element and its rearsubstrate engaging said transfer member, means responsive to thepresence of said receptor between said transfer member and saidphotosensitive element for electrically connecting said rear substratethrough said transfer member to said backing and responsive to theabsence of a receptor between said photosensitive element and transfermember for electrically isolating the front face of said photosensitiveelement from said backing by way of said transfer member and means forelectrically connecting the rear conductive face of a receptor advancingfrom between said photosensitive element and said transfer member tosaid photosensitive element backing.